Goswami A, Weisbecker V, Sánchez-Villagra M R
Department of Earth Sciences, University of Cambridge, Cambridge, United Kingdom.
J Exp Zool B Mol Dev Evol. 2009 May 15;312B(3):186-95. doi: 10.1002/jez.b.21283.
The contrasting evolutionary histories of marsupial and placental mammals have often been attributed to their different reproductive strategies. The speciose placentals develop mainly in utero and have radiated into diverse niches, whereas marsupials are born in a highly altricial state with immediate functional requirements and are limited in taxonomic, ecological, and morphological diversity. These differences have been tied to heterochrony, and it has been hypothesized that coordinated shifts in developmental timing occur among functionally- or developmentally related structures, such as forelimbs in marsupials. We use new ossification sequence data for 11 marsupial and 14 placental species to assess the integration of first ossification timing among skeletal elements. Although cranial elements fail to demonstrate significant coordination, marsupials and placentals differ markedly in postcranial integration. Marsupials display independent anterior and posterior developmental modules, whereas placentals show significant integration of the entire appendicular skeleton. This developmental integration of the placental postcranium is consistent with a recent study of phenotypic modularity in limbs of placental mammals, showing a potential correspondence between integration of developmental timing and of shape. The observed differences in postcranial integration between marsupials and placentals may reflect the disparate evolutionary histories of these two mammalian clades.
有袋类哺乳动物和胎盘类哺乳动物截然不同的进化史常常被归因于它们不同的繁殖策略。种类繁多的胎盘类动物主要在子宫内发育，并已辐射到各种生态位，而有袋类动物出生时处于高度未发育状态，有即时的功能需求，并且在分类学、生态学和形态学多样性方面受到限制。这些差异与异时性有关，并且有人提出，在功能或发育相关的结构之间会发生发育时间的协调变化，如有袋类动物的前肢。我们使用了11种有袋类动物和14种胎盘类动物的新骨化序列数据，以评估骨骼元素之间首次骨化时间的整合情况。虽然颅骨元素未能显示出显著的协调性，但有袋类动物和胎盘类动物在颅后整合方面存在明显差异。有袋类动物表现出独立的前部和后部发育模块，而胎盘类动物则显示出整个附肢骨骼的显著整合。胎盘类动物颅后的这种发育整合与最近一项关于胎盘类哺乳动物肢体表型模块性的研究一致，表明发育时间和形状的整合之间可能存在对应关系。有袋类动物和胎盘类动物在颅后整合方面观察到的差异可能反映了这两个哺乳动物分支不同的进化历史。
